1. Field of the Invention
The present invention relates to a novel non-reducing saccharide, i.e. .alpha.-isomaltosyl .alpha.-isomaltoside (O-.alpha.-D-glucopyranosyl-(1.fwdarw.6)-.alpha.-D-glucopyranosyl O-.alpha.-D-glucopyranosyl-(1.fwdarw.6)-.alpha.-D-glucopyranoside), its preparation and uses. Furthermore, the present invention relates to a composition which contains as an effective ingredient one or more of the novel saccharide and conventionally known .alpha.-isomaltosyl .alpha.-glucoside and .alpha.-isomaltotriosyl .alpha.-glucoside, their preparations and uses.
2. Description of the Prior Art
Trehalose or .alpha.,.alpha.-trehalose is a non-reducing disaccharide consisting of glucose residues and is widely distributed in natural kingdom: For example, trehalose is present in fungi, yeasts, bacteria, mushrooms, higher plants, insects, etc., although the amount is relatively low. Because of its non-reducibility, trehalose neither reacts with substances having amino acid residues such as amino acids and proteins nor causes the Maillard reaction or the amino carbonyl reaction. Therefore, trehalose does not deteriorate amino acid-containing substances. In addition, it is a stable substance and can be freely used and processed without fear of causing browning and deterioration. Thus, trehalose has been expected to be used in a variety of fields. For example, Japanese Patent Laid-Open No.240,758/88 discloses that trehalose is a growth-promoting saccharide for bifid bacteria and is relatively low in cariogenicity. The following researches revealed that trehalose is superior to sucrose on these activities, but the levels of which are relatively low. Therefore, the development of saccharides with higher superiority has been in great demand.
As disclosed in "Chemical & Pharmaceutical Bulletin", Vol.26, pp.3,306-3,311 (1978), isomaltooligosaccharides such as isomaltotriose alias dextrantriose and isomaltotetraose alias dextrantetraose, etc., are known as growth-promoting saccharides for bifid bacteria, and as disclosed in Japanese Patent Publication Nos.39,584/93 and 53,465/93, trehalose is known as a substantially non- or anti-cariogenic saccharide.
However, isomaltooligosaccharides have a reducing activity and readily react with amino acids to cause a browning reaction which deteriorates food products during their preparations. Therefore, the development of superior saccharides has been greatly demanded.
The present inventors concentrated on these properties of trehalose and isomaltooligosaccharides and started to screen saccharides which have an insubstantial reducibility, a selective growth activity for bifid bacteria, and an anti-cariogenicity while expecting greatly the existence of such saccharides among oligosaccharides having trehalose- and isomaltose-structures. As regards such oligosaccharides, Katsumi AJISAKA and Hiroshi FUJIMOTO reported in "Carbohydrate Research", Vol.199, pp.227-234 (1990) that the condensation reaction between trehalose and glucose using .alpha.-glucosidase from a microorganism of the species Saccharomyces sp. or glucoamylase from a microorganism of the species Rhizopus niveus forms .alpha.-isomaltosyl .alpha.-glucoside represented by O-.alpha.-D-glucopyranosyl-(1.fwdarw.6)-.alpha.-D-glucopyranosyl .alpha.-D-glucopyranoside. While Kin et al. reported in "Journal of the Japanese Society of Starch Science", Vol.40, No.3, page 349 (1993) that a saccharide-transferring reaction between dextran and trehalose using isomaltodextranase from Arthrobacter globiformis T6 strain forms .alpha.-isomaltosy .alpha.-glucoside represented by O-.alpha.-D-glucopyranosyl-(1.fwdarw.6)-O-.alpha.-D-glucopyranosyl-(1.fwda rw.6)-.alpha.-D-glucopyranosyl .alpha.-D-glucopyranoside. However, the present inventors noticed that these reports disclose no characteristic property of these saccharides as they need and there has been no report of saccharides having both trehalose- and isomaltose-structures.